Polymer membrane for fuel cell, method of preparing the same, membrane-electrode assembly including the same, and fuel cell system including the same

ABSTRACT

The present invention relates to a polymer electrolyte membrane for a fuel cell, a method for manufacturing the polymer electrolyte membrane, a membrane-electrode assembly for a fuel cell including the polymer electrolyte membrane, and a fuel cell system including the membrane-electrode assembly. The polymer electrolyte membrane includes a proton-conductive polymer membrane including a polymer micelle inside a hydrophilic channel. Herein, the micelle includes a vinyl-based polymer obtained from polymerization of a vinyl-based monomer and an anionic surfactant surrounding the vinyl-based polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a divisional of Applicant's Ser. No. 11/546,392filed in the U.S. Patent & Trademark Office on 12 Oct. 2006, now U.S.Pat. No. 7,659,318, and assigned to the assignee of the presentinvention. Furthermore, this application makes reference to,incorporates the same herein, and claims all benefits accruing under 35U.S.C. §119 from an application for POLYMER MEMBRANE FOR FUELCELL,METHOD OF PREPARING THE SAME, MEMBRANE-ELECTRODE ASSEMBLY COMPRISING THESAME, AND FUEL CELL SYSTEM COMPRISING THE SAME, earlier filed in theKorean Intellectual Property Office on the 12^(th) of October, 2005 andthere duly assigned Serial No. 10-2005-0096071.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymer electrolyte membrane for afuel cell, a method for manufacturing the polymer electrolyte membrane,and a membrane-electrode assembly incorporating the polymer electrolytemembrane for a fuel cell and a fuel cell system incorporating themembrane-electrode assembly. More particularly, the present inventionrelates to a polymer electrolyte membrane having large moistureretention and fuel cross-over inhibition properties and a method formanufacturing the polymer electrolyte membrane, and a membrane-electrodeassembly incorporating the polymer electrolyte membrane for a fuel celland a fuel cell system incorporating the membrane-electrode assembly.

2. Description of the Related Art

A fuel cell is a power generation system for producing electrical energythrough an electrochemical redox reaction between an oxidant and a fuelsuch as hydrogen, or a hydrocarbon-based material such as methanol,ethanol, and natural gas.

Such a fuel cell is a clean energy source that can replace fossil fuels.The fuel cell is typically constructed with a stack composed of unitcells that produces various ranges of power output. Since it has anapproximately four to ten times higher energy density than a smalllithium battery, it has been highlighted as a small portable powersource.

Representative exemplary fuel cells include a polymer electrolytemembrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). Thedirect oxidation fuel cell includes a direct methanol fuel cell thatuses methanol as a fuel.

The polymer electrolyte fuel cell has advantages of high energy densityand high power, but it also has problems in the need for exceptionallycareful handling of hydrogen gas and in its requirement for accessoryfacilities such as a fuel reforming processor for reforming methane ormethanol, natural gas, and the like in order to produce hydrogen as thefuel gas.

On the contrary, a direct oxidation fuel cell has a lower energy densitythan that of the gas-type fuel cell but has the advantages of easyhandling of the liquid-type fuel, a low operation temperature, and noneed for additional fuel reforming processors. Therefore, it has beenacknowledged as an appropriate system for a portable power source forsmall and common electrical equipment.

In the above-mentioned fuel cell system, the stack that generateselectricity substantially includes several to scores of unit cellsstacked adjacent to one another, and each unit cell is constructed witha membrane-electrode assembly (MEA) and a separator (also referred to asa bipolar plate). The membrane-electrode assembly is constructed with ananode (also referred to as a “fuel electrode” or an “oxidationelectrode”) and a cathode (also referred to as an “air electrode” or a“reduction electrode”) that are separated by a polymer electrolytemembrane.

A fuel is supplied to the anode and is adsorbed on catalysts of theanode, and the fuel is oxidized to produce protons and electrons. Theelectrons are transferred into the cathode via an 11 external circuit,and the protons are transferred into the cathode through the polymerelectrolyte membrane. In addition, an oxidant is supplied to thecathode, and then the oxidant, protons, and electrons react on thecatalyst of the cathode to produce electricity along with water.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved fuel cell system.

It is another object to provide an improved polymer electrolyte membranefor a fuel cell system.

It is yet another object to provide a polymer electrolyte membranehaving smaller, but more densely distributed internal channels toimprove proton conductivity and to suppress cross-over of a fuel throughthe polymer electrolyte membrane.

It is still another object to provide a polymer electrolyte membrane fora fuel cell that includes polymer micelles inside a water ion clusterthat thereby improve moisture retention and fuel cross-over inhibitionproperties.

It is still yet another object to provide a method for manufacturing thepolymer electrolyte membrane using an emulsion polymerization.

It is a further object to provide a membrane-electrode assemblyincluding the polymer electrolyte membrane.

It is a still further object to provide a fuel cell system including thepolymer electrolyte membrane for a fuel cell.

According to one embodiment of the present invention, a polymerelectrolyte membrane is provided with a polymer micelle inside ahydrophilic channel of a proton-conductive polymer membrane. The polymermicelle includes a vinyl-based polymer obtained from polymerization ofvinyl-based monomers and an anionic surfactant surrounding thevinyl-based polymer.

According to another embodiment of the present invention, a method formanufacturing a polymer electrolyte membrane is provided to prepare anemulsion polymerization solution by mixing a vinyl-based monomer, ananionic surfactant, and a radical polymerization initiator in water, todip a proton-conductive polymer membrane in the emulsion polymerizationsolution to swell the membrane, and to perform an emulsionpolymerization of the monomer embedded inside the swelledproton-conductive polymer membrane to form a polymer micelle.

According to yet another embodiment of the present invention, amembrane-electrode assembly for a fuel cell is provided with thispolymer electrolyte membrane, a cathode at one side of the polymerelectrolyte membrane, and an anode at the other side of the polymerelectrolyte membrane.

According to still another embodiment of the present invention, a fuelcell system is provided with an electricity generating element, a fuelsupplier, and an oxidant supplier. The electricity generating elementincludes a membrane-electrode assembly and a separator positioned oneach side of the membrane-electrode assembly. The membrane-electrodeassembly includes this polymer electrolyte membrane, a cathode at oneside of the polymer electrolyte membrane, and an anode at the other sideof the polymer electrolyte membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a schematic diagram illustrating a polymer micelle includedinside a hydrophilic channel of a polymer electrolyte membrane as oneembodiment according to the principles of the present invention.

FIG. 2 is a single line schematic diagram illustrating the structure ofa fuel cell system constructed as another embodiment according to theprinciples of the present invention.

FIG. 3 is a schematic diagram illustrating the structure of amembrane-electrode assembly incorporating the polymer electrolytemembrane as still another embodiment according to the principles of thepresent invention.

FIG. 4 is a schematic diagram illustrating the structure of the polymerelectrolyte membrane as the embodiment according to the principles ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In a fuel cell system, a fuel is supplied to an anode and is adsorbed oncatalysts of the anode, and the fuel is oxidized to produce protons andelectrons. The electrons are transferred into a cathode via an externalcircuit, and the protons are also transferred into the cathode throughthe polymer electrolyte membrane. In addition, an oxidant is supplied tothe cathode, and then the oxidant, protons, and electrons react on thecatalyst of the cathode to produce electricity along with water. Theelectrochemical reactions between the fuel and the oxidant can berepresented by the following formulas.Anode: H₂→2H⁺+2e ⁻Cathode: ½O₂+2H⁺+2e ⁻→H₂OTotal: H₂+½O₂→H₂O+electric current+heat  [Formula 1]

A direct oxidation fuel cell (DOFC), in particular, a direct methanolfuel cell which uses methanol as a fuel, is commonly constructed with aNAFION-based (NAFION™ is available from E.I. DuPont de Nemours and Co.)membrane as a polymer electrolyte membrane. When methanol in a highconcentration is used as a fuel, however, it may cross over theNAFION-based membrane, thereby deteriorating the battery's performance.In addition, the NAFION-based membrane can be swollen by the fuel thatcrosses over the membrane, and the catalyst of the cathode may be peeledoff from the NAFION-based membrane by the over-crossed fuel.

Exemplary embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

According to an embodiment of the present invention, a polymerelectrolyte membrane for a fuel cell includes a micelle inside ahydrophilic channel of the proton-conductive polymer membrane. Themicelle refers to an aggregate of surfactant molecules in which severalto tens of surfactant molecules are stably dispersed with a hydrophobicgroup consisting of the molecule disposed inward and a hydrophilic groupconsisting of the molecule disposed outward, since the absorption of ahydrophilic material and a hydrophobic material is saturated on theinterface between the hydrophilic material and the hydrophobic material,and also, excessive surfactant molecules in water decrease resistancebetween the water and the hydrophobic material when the surfactantreaches a concentration. The surfactant refers to a wetting agent thatlowers the surface tension of a liquid, allowing easier spreading of theliquid, and lower the interfacial tension between two liquids.

A micelle is formed when a variety of molecules are added to water. Themolecule must have a strongly polar “head” and a non-polar hydrocarbonchain “tail”. When this type of molecule is added to water, thenon-polar tails of the molecules clump into the center of a ball likestructure which is called a micelle, because they are hydrophobic or“water hating”. The polar heads of the molecules presents themselves forinteraction with the water molecules on the outside of the micelle. Atypical micelle in aqueous solution forms a roughly spherical orglobular aggregate with the hydrophilic “head” regions in contact withsurrounding solvent, sequestering the hydrophobic tail regions in themicelle center. Micelles are often globular and roughly spherical inshape, but ellipsoids, cylinders, and bi-layers are also possible. Theshape of a micelle is a function of the molecular geometry of itssurfactant molecules and solution conditions such as surfactantconcentration, temperature, pH, and ionic strength. Individualsurfactant molecules that are in the colloid but are not part of amicelle are called “monomers”. In water, the hydrophilic “heads” ofsurfactant molecules are always in contact with bulk solvent, regardlessof whether the surfactants exist as monomers or as part of a micelle.However, the hydrophobic “tails” of surfactant molecules have lesscontact with water when they are part of a micelle. In a micelle, thehydrophobic tails of several surfactant molecules assemble into anoil-like core that has less contact with water.

In general, when a polymer electrolyte membrane, particularly aNAFION-based membrane, is swollen by water, a water ionic cluster (WIC)is formed in an inverse micelle structure, in which hydrophilic —SO₃ ⁻ions are attached to a main chain of a polymer and surround a waterpool. An inverse micelle structure indicates a molecular aggregate inwhich the molecules are dispersed with a hydrophilic group inward and ahydrophobic group outward. The water ionic cluster (WIC) permeates intothe polymer electrolyte membrane, and then forms a hydrophilic channel,which is a hydrogen ion conductive channel, for transferring a protontherethrough. When the channel becomes large, however, a fuel from theanode of the membrane-electrode assembly may cross over the polymerelectrolyte membrane to the cathode, due to the osmosis drag phenomenon.Osmosis drag is a phenomenon in which water molecules from a region ofhigh potential flow across a partially permeable membrane and into aregion of low potential. The partially permeable membrane is permeableto the solvent of the fuel, i.e., water, but is not permeable to thesolute.

FIG. 1 schematically shows a polymer micelle included inside ahydrophilic channel of a polymer electrolyte membrane one embodimentaccording to the principles of the present invention. As shown in FIG.1, a polymer micelle 100 contains a vinyl-based polymer 110 and ananionic surfactant 120 surrounding vinyl-based polymer 110. In addition,polymer micelle 100 is surrounded with water in a hydrophilic channel130. Anionic surfactant 120 includes a hydrophobic part 121 facinginwardly toward the center of polymer micelle 100 and a hydrophilic part122 facing outwardly from the center of polymer micelle 100.

Micelle 100 has an average particle diameter ranging from 1 nm to 10 μm.When the size of micelle 100 is less than 1 nm, micelle 100 might beeasily discharged with water through hydrophilic channel 130, while whenmore than 10 μm, micelle 100 may block hydrophilic channel 130, so thatwater and protons cannot flow smoothly.

Micelle 100 functions as a barrier to prevent cross-over of a fuelinside hydrophilic channel 130 of the polymer electrolyte membranebecause micelle 100 is constructed with a surfactant having ahydrophilic ion group, which may strongly combine with water moleculesand, thereby, may hold water.

Vinyl-based polymer 110 constituting micelle 100 is obtained frompolymerization of vinyl-based monomers such as styrene, alpha-methylstyrene, 4-methylstyrene, 3,4-dichlorostyrene, methyl metacrylic acid,sodium acrylamide-tert-butyl sulfonate, polyaniline, polypyrrol, andpoly thiophene.

Vinyl-based polymer 110 has an average molecular weight ranging from1000 to 100000. When the average molecular weight of vinyl-based polymer110 is less than 1000, the size of micelle 100 is too small to be fixedin the membrane, whereas when the average molecular weight ofvinyl-based polymer 110 is more than 100000, vinyl-based polymer 110 maybe coated on the surface of the polymer electrolyte membrane.

Anionic surfactant 120 constituting micelle 100 may be made from atleast one selected from the group consisting of an alkyl fatty acid saltincluding a C1 to C20 alkyl, an alkylsulfonate including a C1 to C12alkyl, an alcohol sulfuric acid ester salt including a C1 to C12 alkyl,an alkyl arylsulfonate including a C1 to C12 alkyl, and combinations ofthese materials. According to one embodiment, a stearic acid(octadecanoic acid) or an alkylsulfonate including a C1 to C12 alkyl maybe preferably used.

The polymer electrolyte membrane is made from any proton-conductivepolymer that is usually incorporated in a fuel cell.

The proton-conductive polymer may include at least one selected from thegroup consisting of fluoro-based polymers, benzimidazole-based polymers,polyimide-based polymers, polyetherimide-based polymers,polyphenylenesulfide-based polymers, polysulfone-based polymers,polyethersulfone-based polymers, polyetherketone-based polymers,polyether-etherketone-based polymers, and polyphenylquinoxaline-basedpolymers. In a preferred embodiment, the proton-conductive polymerincludes at least one selected from the group consisting ofpoly(perfluorosulfonic acid) (NAFION™), poly(perfluorocarboxylic acid),a copolymer of tetrafluoroethylene and fluorovinylether having asulfonic acid group, defluorinated polyetherketone sulfide, aryl ketonehaving a proton-conductive functional group,poly(2,2′-(m-phenylene)-5,5′-bibenzimidazole) having a proton-conductivefunctional group, poly(2,5-benzimidazole) having a proton-conductivefunctional group, and mixtures of these polymers.

The proton-conductive functional group may include at least one selectedfrom the group consisting of sulfonic acid, sulfonate, carboxylic acid,carboxylate, phosphoric acid, and phosphate.

Polymer micelle 100 is included in the proton-conductive polymer in anamount of 5 to 50 parts by weight based on 100 parts by weight of theproton-conductive polymer. When polymer micelle 100 is included in anamount of less than 5 parts by weight, it may have little effect, whilewhen in an amount of more than 50 parts by weight, it is practicallyimpossible to prepare.

The polymer electrolyte membrane is prepared as follows: a vinyl-basedmonomer, an anionic surfactant, and a radical polymerization initiatorare mixed in water to prepare an emulsion polymerization solution; aproton-conductive polymer membrane is dipped in the emulsionpolymerization solution to swell the membrane; and an emulsionpolymerization of the monomer embedded inside the swelledproton-conductive polymer membrane is performed to form a polymermicelle.

The anionic surfactant of the emulsion polymerization solution mayinclude at least one selected from the group consisting of an alkylfatty acid salt including a C1 to C20 alkyl, an alkylsulfonate includinga C1 to C12 alkyl, an alcohol sulfuric acid ester salt including a C1 toC12 alkyl, an alkyl arylsulfonate including a C1 to C12 alkyl, andcombinations thereof.

The radical polymerization initiator is not specifically limited to, butmay be selected from the group consisting of a peroxide-based compound,a hydroperoxide-based compound, an azo-based compound, and combinationsthereof.

The emulsion polymerization is performed while dipping theproton-conductive polymer membrane in the emulsion polymerizationsolution at the temperature of 0 to 50° C. for between 1 to 10 hours.

According to another embodiment according to the principles of thepresent invention, the membrane-electrode assembly is constructed withthe above polymer electrolyte membrane and an anode and a cathodedisposed on each side of the polymer electrolyte membrane.

Each of the cathode and the anode includes an electrode substrate and acatalyst layer. The catalyst layer may contain platinum, ruthenium,osmium, platinum-ruthenium alloys, platinum-osmium alloys,platinum-palladium alloys, platinum-M alloys, or combinations thereof,where M is a transition element selected from the group consisting ofGa, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh, and combinationsthereof.

According to one embodiment, platinum-based catalysts may contain Pt,Pt/Ru, Pt/W, Pt/Ni, Pt/Sn, Pt/Mo, Pt/Pd, Pt/Fe, Pt/Cr, Pt/Co, Pt/Ru/W,Pt/Ru/Mo, Pt/Ru/V, Pt/Fe/Co, Pt/Ru/Rh/Ni, Pt/Ru/Sn/W, and a combinationthereof.

The metal catalyst layer may be supported on a carrier or may be a blacktype catalyst that is not supported on a carrier. The carrier mayinclude carbon-based materials such as graphite, denka black, ketjenblack, acetylene black, carbon nanotube, carbon nano fiber, carbon nanowire, carbon nano ball, or activated carbon, or an inorganic particulatesuch as alumina, silica, zirconia, or titania may also be used. Acarbon-based material is generally used as a carrier.

The electrode substrate functions to support an electrode, and also tospread a fuel or an oxidant to the catalyst layers to help the fuel andthe oxidant to easily approach the catalyst layers. For the electrodesubstrates, a conductive substrate is used, for example carbon paper,carbon cloth, carbon felt, or metal cloth (a porous film including ametal cloth fiber or a metalized polymer fiber), but the presentinvention is not limited thereto.

The electrode substrate may be treated with a fluorine-based resin to bewater-repellent, which can prevent the deterioration of reactantdiffusion efficiency due to water generated during fuel cell operation.The fluorine-based resin includes polyvinylidene fluoride,polytetrafluoroethylene, fluorinated ethylene propylene,polychlorotrifluoroethylene, fluoroethylene polymers, and so on.

A microporous layer (MPL) can be added between the aforementionedelectrode substrate and the catalyst layer to increase reactantdiffusion efficiency. The microporous layer generally includesconductive powders with a particle diameter. The conductive material mayinclude, but is not limited to, carbon powder, carbon black, acetyleneblack, activated carbon, carbon fiber, fullerene, nano-carbon, orcombinations thereof. The nano-carbon may include a material such ascarbon nanotubes, carbon nanofiber, carbon nanowire, carbon nanohorns,carbon nanorings, or combinations thereof. The microporous layer isformed by coating a composition including a conductive powder, a binderresin, and a solvent on the conductive substrate. The binder resin mayinclude, but is not limited to, polytetrafluoro ethylene, polyvinylidenefluoride, polyvinyl alcohol, cellulose acetate, polyhexafluoropropylene, polyperfluoroalkylvinyl ether, polyperfluoro sulfonylfluoridealkoxy vinyl ether, and copolymers thereof. The solvent may include, butis not limited to, an alcohol such as ethanol, isopropylalcohol,n-propylalcohol, butanol, and so on, water, dimethyl acetamide, dimethylsulfoxide, or N-methylpyrrolidone. The coating method may include, butis not limited to, screen printing, spray coating, doctor blade methods,gravure coating, dip coating, silk screening, painting, and so on,depending on the viscosity of the composition.

FIG. 2 shows a single line schematic diagram of a fuel cell systemconstructed as an embodiment according to the principles of the presentinvention, that will be described in detail with reference to thisaccompanying drawing as follows. FIG. 2 illustrates a fuel cell system200 wherein a fuel and an oxidant are respectively provided toelectricity generating element 219 through pumps 211 and 213, but thepresent invention is not limited to such structure. Alternatively, thefuel cell system of the present invention may be constructed as astructure wherein a fuel and an oxidant are provided in a diffusionmanner. FIG. 3 shows a schematic diagram illustrating the structure of amembrane-electrode assembly constituting the fuel cell system as shownin FIG. 2. FIG. 4 shows a schematic diagram illustrating the structureof the polymer electrolyte membrane as an embodiment according to theprinciples of the present invention.

Fuel cell system 200 is constructed with a stack 207 including at leastone electricity generating element 219 that generates electrical energythrough an electrochemical reaction between a fuel and an oxidant, afuel supplier 201 for supplying a fuel to electricity generating element219, and an oxidant supplier 205 for supplying an oxidant to electricitygenerating element 219.

In addition, fuel supplier 201 is equipped with a tank 209 that stores afuel, and a pump 211 that is connected therewith. Fuel pump 211 suppliesthe fuel stored in tank 209 with a pumping power.

The fuel includes liquid or gaseous hydrogen, or a hydrocarbon-basedfuel such as methanol, ethanol, propanol, butanol, or natural gas.

Oxidant supplier 205 of fuel cell system 200, which supplies theelectricity generating element 219 with an oxidant, is equipped with atleast one pump 213 for supplying an oxidant with a pumping power.

Electricity generating element 219 is constructed with amembrane-electrode assembly 221 that oxidizes hydrogen or the fuel andreduces the oxidant, and separators 223 and 225 that are respectivelypositioned on opposite sides of membrane-electrode assembly 221 andsupply hydrogen or the fuel, and the oxidant. As shown in FIG. 3,membrane-electrode assembly 221 is constructed with the aforementionedpolymer electrolyte membrane 310, and a cathode 330 and an anode 320disposed on opposite sides of polymer electrolyte membrane 310. Theelectricity generating element generates electricity through oxidationof a fuel and reduction of an oxidant.

The following examples illustrate the present invention in more detail.It is understood, however, that the present invention is not limited bythese examples.

Example 1

30 g of styrene, 0.5 g of azobisisobutyronitrile (AIBN) as a radicalinitiator, and 10 g of dodecylbenzenesulfonic acid (DBSA) as an anionicsurfactant were put in 200 g of deionized water (DW) and mixedtherewith, thereby preparing an emulsion polymerization solution.

Then, a 0.005 inch thick NAFION 115 (NAFION® 115) membrane (Dupont Co.)was dipped into the polymerization solution, so that it can besufficiently swollen by the emulsion polymerization solution andpermeated thereby.

The swollen NAFION membrane was left in the emulsion polymerizationsolution at 30° C. for 10 hours and then was washed, thereby preparing apolymer electrolyte membrane.

Comparative Example 1

The same NAFION 115 (NAFION® 115) membrane as in Example 1 was used as apolymer electrolyte membrane.

Then, the polymer electrolyte membranes for a fuel cell fabricatedaccording to Example 1 and Comparative Example 1 were evaluatedregarding proton conductivity, swelling characteristics, andpermeability by the over-crossed amount of methanol.

The proton conductivity was measured by using a 2-probe type impedanceanalyzer (IM6, BAS-Zahner Instruments), and the swelling characteristicwas estimated by measuring weight change of distilled water afterswelling. In addition, the permeability was estimated by measuring theover-crossed amount of methanol cross-over with a refractometer.

The results are provided in the following Table 1.

TABLE 1 Example 1 Comparative Example 1 Proton conductivity (S/cm) 0.190.1 Swelling characteristic (%) 10 15 Permeability (cm²/s) 1.51.3 × 10²⁵1.3 × 10²⁶

As shown in Table 1, the polymer electrolyte membrane of Example 1turned out to have more excellent proton conductivity and swellingcharacteristic, and also have less methanol permeability than that ofComparative Example 1.

Therefore, the polymer electrolyte membrane according to the principlesof the present invention, which is constructed with a polymer micelleincluding a polymer and a surfactant surrounding the polymer inside ahydrophilic channel, can decrease cross-over of a fuel and solve thelack of water therein since the surfactant has high affinity to water.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method for manufacturing a polymer electrolyte membrane,comprising: preparing an emulsion polymerization solution by mixing avinyl-based monomer, an anionic surfactant, and a radical polymerizationinitiator in water; dipping a proton-conductive polymer membrane in theemulsion polymerization solution to swell the membrane; and performingan emulsion polymerization of the monomer embedded inside the swelledproton-conductive polymer membrane to form a polymer micelle.
 2. Themethod of claim 1, comprised of the vinyl-based monomer comprising oneselected from the group consisting of styrene, alpha-methyl styrene,4-methylstyrene, 3,4-dichlorostyrene, methyl metacrylic acid, sodiumacrylamide-tert-butyl sulfonate, polyaniline, polypyrrol, polythiophene, and combinations thereof.
 3. The method of claim 1, comprisedof the anionic surfactant comprising at least one selected from thegroup consisting of an alkyl fatty acid salt including a C1 to C20alkyl, an alkylsulfonate including a C1 to C12 alkyl, an alcoholsulfuric acid ester salt including a C1 to C12 alkyl, an alkylarylsulfonate including a C1 to C12 alkyl, and combinations thereof. 4.The method of claim 1, comprised the radical polymerization initiatorcomprising one selected from the group consisting of a peroxide-basedcompound, a hydroperoxide-based compound, an azo-based compound, andcombinations thereof.
 5. The method of claim 1, comprised of performingthe emulsion polymerization at 0 to 50° C. while dipping theproton-conductive polymer membrane in the emulsion polymerizationsolution.
 6. A membrane-electrode assembly for a fuel cell, comprising:a polymer electrolyte membrane comprising a polymer micelle inside ahydrophilic channel of a proton-conductive polymer membrane, with thepolymer micelle comprising a vinyl-based polymer obtained frompolymerization of vinyl-based monomers and an anionic surfactantsurrounding the vinyl-based polymer; a cathode formed on one side of thepolymer electrolyte membrane; and an anode formed on the other side ofthe polymer electrolyte membrane.